Sensors provide a wealth of information to the people and equipment that utilize their readings. A common use of sensors is for automotive applications. In an automobile, sensors provide information on the speed of the car, condition of the engine, amount of fuel available, and even outside environmental conditions.
During the operation of an automobile, it is highly desirable to ensure that the tires are properly inflated. The safety of the vehicle occupants and the vehicle depends on having the tires properly inflated. In the event that the tires are not properly inflated, severe damage can occur to the tires. This damage to the tires can result in great harm, even death to the vehicle occupants. For instance, the various layers forming the tire can separate causing the tire to fail structurally. Alternatively, an over-inflated tire that encounters a road obstacle such as a rock can burst. It therefore becomes highly desirable to monitor the pressure of the tires to ensure that they are properly inflated.
More specifically, during normal operation at a constant temperature, tires can lose air pressure at the rate of one psi per month. Additionally, tires can lose air pressure at the rate of one psi for every 10 degrees Fahrenheit temperature drop. Tires that are under inflated are less able to support weight than properly inflated tires. An exemplary weight for a sport utility vehicle is 6540 pounds. An exemplary set of tires, properly inflated at 30 psi, can support 6540 pounds, thereby safely carrying the SUV. However, these tires only have a carrying capacity of 5610 pounds if they are inflated to 20 psi. Consequently, when under inflated at 20 psi, the tires are overloaded by 1230 pounds. This under inflation and overloading of the tires can lead to serious, if not deadly consequences on the highway.
Further, a lower than desired air pressure within the tire during operation increases the heat within the tire walls during operation. This heat increases as the speed of the vehicle increases. At high speeds on a highway, the heat can reach such a level within under inflated tires that the various layers forming the tire separate from each other. This separation can lead to a car accident injuring the occupants of the vehicle and potentially the occupants of other vehicles as well. As a matter of safety, to protect the lives of the vehicle occupants, it becomes highly desirable to place pressure sensors in each tire to monitor the air pressure and display the real time pressure readings on the dashboard for the vehicle driver. Through providing the driver with real time air pressure information, the driver can properly maintain the air pressure of the tires and safely operate the vehicle.
Aside from safety, the air pressure of the tires also affects the vehicle fuel efficiency. Properly inflated tires lead to greater fuel efficiency than when tires are under-inflated. Therefore, in addition to safety, fuel efficiency is another reason that it is highly desirable to monitor the pressure of the tires.
Placing a pressure sensor in a tire to monitor the air pressure presents several technical challenges. The environment within the tire is highly corrosive to solid state pressure sensors. As protection to this corrosive environment, internal tire pressure sensors are provided with various coatings, encapsulant, or diaphragms made from various elastic gels, polymers, or other materials.
As a component that is placed in each and every tire, it is highly desirable to minimize the cost of the tire pressure sensor. Through simplifying the design, manufacture, and components of the tire pressure sensor, it is possible to reduce the sensor cost.
In addition to automotive uses, sensors provide valuable information for commercial and industrial applications. These applications include, but are not limited to medical uses, biological and chemical monitors for research and manufacturing, as well as any fluid or gaseous environmental monitors.